23.3.10.1. ##/#

mytar.sh
#!/bin/bash
if [ "${1##*.}" = "tar" ]
then
echo This appears to be a tarball.
else
echo At first glance, this does not appear to be a tarball.
fi
$ ./mytar.sh thisfile.tar
This appears to be a tarball.
$ ./mytar.sh thatfile.gz
At first glance, this does not appear to be a tarball.